In general, this invention relates to video reproduction apparatus in which video information is recorded in a plurality of longitudinal tracks on magnetic tape along with a timing signal recorded in a timing track parallel to the video information tracks. More particularly, this invention relates to video reproduction apparatus in which dropouts in the reproduced timing signal are compensated so that degradation of a reproduced video image caused by such dropouts are reduced.
Although most video reproduction devices utilize a spinning magnetic head to record video information on magnetic tape in tracks which run either substantially perpendicular to the direction of travel of the tape or at an angle to the direction of travel of the tape, various video reproduction devices have been proposed in which the video information is recorded in a plurality of parallel tracks which run longitudinally in the direction of tape movement. Such longitudinal reproduction devices have been especially useful in the motion analysis of fast moving phenomena in slow motion. Such a motion analyzer device is disclosed in commonly-assigned U.S. Pat. No. 4,496,995, issued Jan. 29, 1985. As disclosed therein, the motion analyzer entails the recording of a great number of images during an event at high tape speed and high frame rate, and reproducing the images more slowly at a lower frame rate and lower tape speed to analyze the movement which has occurred in step by step progression. Applications for such a motion analysis system include malfunctions in high speed machinery, movements of an athlete, testing of safety equipment, shattering of an object, etc. As disclosed in the latter patent, the motion analyzer includes a video camera, a variable speed magnetic tape processor and a video display monitor. The camera is read out in block format so that a plurality of lines of video information that correspond to rows of photosites in the camera are simultaneously recorded on magnetic tape in longitudinal parallel tracks. In order to play back the video signals recorded in the plurality of parallel tracks and to convert the parallel signals into a sequential signal which may be used with standard video monitors, a timing track is recorded parallel to the video information tracks at the time of recording. Upon playback, the timing signal is reproduced and processed to effect synchronous timing and control of the reproduced video signal.
Ideally, to effectively reproduce the timing signal and video information from the tape, the tape is moved past the playback head at a constant speed over the length of the recorded video signal. In reality, such ideal conditions are difficult to achieve and timing errors which may result in severely degraded or totally incomprehensable video displayed information may occur. Thus, variations in the speed of the tape moving past the playback head may be caused by localized tape stretch, tape vibration, and/or fluctuations in the speed of the tape transport mechanism. This timing error called flutter occurs in both the video information and simultaneously in the timing signal played back from the timing track. Since the timing signal is used to process the video information reproduced from the video tracks, the timing signal processing circuitry should be effective in following the flutter in tape so that the frequency of the timing signal will change proportionately to the flutter and recovery of video information from the tape will change proportionately. Difficulty arises, however, when the timing signal processing circuitry is not compensated to take into account dropouts in the timing track, which could effect poor recovery of the video information and severe degradation in the quality of the reproduced scene.